The requested spectropolarimeter (Jasco J-500C) will be used for various circular dichroism studies dealing with: (1) the interactions of the various proteins of the blood coagulation cascade (thrombin, antithrombin III, Factor IX, Factor X); (2) interactions of heparin with antithrombin III using heparin derivatives and heparin octasaccharide; (3) interactions of protein synthesis initiation factors (eIF-2, Met-tRNA); and (4) structure and function studies of thyroxine-binding globulin (TBG), the major transport protein of the thyroid hormones. In all these studies, there is a great need for a conformation-sensitive tool to detect changes during the interactions of these various macromolecules. There is no doubt the requested spectropolarimeter will meet this need and enhance the planned research endeavors of these investigators. The existence of conformational changes associated with thrombin-antithrombin III and heparin-antithrombin III interactions have been well-documented, but the detailed aspects of the nature of these conformational changes are not clear. Studies on the conformation of heparin in solution have been very limited. The conformational changes associated with the phosphorylation of eIF-2 leading to inhibition of protein synthesis have been postulated but direct experimental evidence is lacking. It is expected that the proposed conformational studies on antithrombin III-thrombin reaction will provide information for better understanding of the complex functions of antithrombin III and better insights into the mechanism by which heparin and antithrombin III affect blood coagulation. The detailed studies proposed for the conformation of heparin in solution should provide the much needed information about the true conformation of heparin in solution, and for that matter, of the mucopolysaccharides in general. The proposed research on protein initiation factors should contribute to our understanding of the mechanism of translation and translational inhibition of protein synthesis. As a whole, the long term efforts of these studies are expected to yield information essential to our understanding of the conformational aspects of protein-protein, protein-nucleic acid and protein-mucopolysaccharide interactions.